Since India ink is made from carbon particles, these form a percolation network of low conductivity when the ink dries. Thus, India ink allows attachment of wires to measurement specimens when a highly conductive attachment is not required. It is especially useful in high voltage circuitry to allow a very high resistance ground return for components.

Ink is nearly ubiquitous among cephalopods, so a natural question would be when such an evolutionary adaptation got started, and whether ancient cephalopod ink was different from modern ink. The problem here is that you need a specimen of primordial ink. A large international team of scientists has analyzed traces of ink from two ink sacks associated with fossils of 160-million-year-old giant cephalopods from the Jurassic period.[1-2] The fossils were discovered two years ago in England.[1]

That melanin, an organic compound, should survive after 160 million years, seems quite remarkable, since animal tissue decomposes quickly. Melanin, however, is more resistant to decomposition, since it's polymeric. Says Simon,

"Out of all of the organic pigments in living systems, melanin has the highest odds of being found in the fossil record... Though the other organic components of the cephalopod we studied are long gone, we've discovered through a variety of research methods that the melanin has remained in a condition that could be studied in exquisite detail."[1]

The chemical composition of the trace evidence of melanin matched the melanin of modern cuttlefish ink. This affirms the possibility that the ink cloud defense mechanism of such creatures hasn't changed since the Jurassic. Says Simon, "The whole machinery apparently has been locked in time and passed down through succeeding generations of cuttlefish. It's a very optimized system for this animal and has been optimized for a long time."[1]